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(#) Invalid format string

!!! ERROR: Invalid format string
   This is an error.

Id
:   `StringFormatInvalid`
Summary
:   Invalid format string
Severity
:   Error
Category
:   Correctness: Messages
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Resource files
Editing
:   This check can *not* run live in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/StringFormatDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/StringFormatDetectorTest.java)
Copyright Year
:   2011

If a string contains a '%' character, then the string may be a
formatting string which will be passed to `String.format` from Java code
to replace each '%' occurrence with specific values.

This lint warning checks for two related problems:
(1) Formatting strings that are invalid, meaning that `String.format`
will throw exceptions at runtime when attempting to use the format
string.
(2) Strings containing '%' that are not formatting strings getting
passed to a `String.format` call. In this case the '%' will need to be
escaped as '%%'.

NOTE: Not all Strings which look like formatting strings are intended
for use by `String.format`; for example, they may contain date formats
intended for `android.text.format.Time#format()`. Lint cannot always
figure out that a String is a date format, so you may get false warnings
in those scenarios. See the suppress help topic for information on how
to suppress errors in that case.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/StringFormatInvalid.java:3:Error: Format string 'no_args' is not a
valid format string so it should not be passed to String.format
[StringFormatInvalid]
    context.getString(R.string.no_args, "first"); // ERROR
    --------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/StringFormatInvalid.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
public class StringFormatInvalid {
    public static void testContext(android.content.Context context) {
        context.getString(R.string.no_args, "first"); // ERROR
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`res/values/strings.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;resources&gt;
    &lt;string name="no_args"&gt;Hello&lt;/string&gt;
&lt;/resources&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/StringFormatDetectorTest.java)
for the unit tests for this check to see additional scenarios.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="StringFormatInvalid" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'StringFormatInvalid'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore StringFormatInvalid ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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